As shown in FIGS. 8 and 9, a travel mug of the prior art comprises an inner case 70, an outer case 71, a thermal insulation material 72, and a heating coil 74. The inner case 70 is made of a plastic material and is fitted into the outer case 71 along with the thermal insulation material 72 which is located between the inner case 70 and the outer case 71. The inner case 70 is provided at the bottom end with an aluminum foil cover 73 which is encircled by the heating coil 74. The heating coil 74 is connected to a power source cord 76 via a through hole 75 of the outer case 71.
Such a prior art travel mug as described above is defective in design in that the assembly of the travel mug is done along with the aluminium foil cover 73 and the thermal insulation material 72, thereby resulting in an increase in production cost. In addition, the heating efficiency is poor due to the limited contact between the aluminum foil cover 73 and the heating coil 74.
The inner case 70 is vulnerable to damage caused by heat in the event that it is inadvertently kept empty while being heated. Moreover, the power source cord 76 is inseparably attached to the outer case 71 and is therefore bothersome during packing.